1. Field of the Invention
The present invention relates to a magnetic head, and more particularly to an induction-type magnetic head having a first magnetic core and a second magnetic core disposed in the vicinity of the first magnetic core and generating a magnetic flux larger than that of the first magnetic core
2. Description of the Prior Art
As an example of this type of magnetic head, known is a so-called tunnel erasing type magnetic head used in a magnetic disc apparatus for recording and/or reproducing data on and/or from a magnetic recording medium such as a magnetic disc and having a recording and/or reproducing core and an erasing core for erasing both outside portions of a track on which recording has been performed by the recording and/or reproducing core, the cores being disposed close to each other along a rotating direction of the magnetic disc.
An arrangement of a conventional tunnel erasing type magnetic head is constructed as shown in FIGS. 1 and 2 or in FIG. 3.
FIGS. 1 and 2 show a magnetic head having a core arrangement known generally as a bulk type.
In FIG. 1, reference numerals 1a and 1b denote respectively front core halves of a recording and/or reproducing core 1. The front core halves 1a and 1b have upper edge portions adhered to each other. A magnetic gap 2 for recording and/or reproducing is formed in the adhesion portion exposed in an upper edge surface that is disposed opposite a magnetic disc. An adhesive such as adhesive glass 2a is exposed on both sides of the magnetic gap 2. The distance between the adhesives 2a and 2a corresponds to the width of the recording and/or reproducing track. Reference numerals 3a and 3b denote front core halves of an erasing core 3. The front core halves 3a and 3b are adhered to each other in the same manner, and magnetic gaps 4 and 4' for erasing are formed on both outside portions of the adhesion portion exposed on an opposing surface thereof which is to face the magnetic disc.
An adhesive 4a such as adhesive glass is exposed between the magnetic gaps 4 and 4'. The width between the adhesives 4a and 4a is substantially the same as the distance between the above-mentioned adhesives 2a and 2a.
The core halves 1b and 3b are adhered to each other via a spacer plate 5 made of a non-magnetic material such as glass or ceramic, so that the pairs of the core halves 1a and 1b, and 3a and 3b are integrated. In this arrangement, the erasing magnetic gaps 4 and 4' are disposed to sandwich the recording and/or reproducing magnetic gap 2 when seen along the rotating direction of a disc not shown.
Of the core halves 1a and 1b, and 3a and 3b which have been integrated in this manner, a bobbin 7 having a coil 8 wound therearound is inserted into the core half 1a and a bobbin 9 having a coil 10 wound therearound is inserted into the core half 3a.
Furthermore, a compound back core 6 is formed integrally by a spacer plate 6c made from a non-magnetic material being sandwiched by back cores 6a and 6b. The spacer plate 6c is disposed at a position corresponding to that of the spacer plate 5. The back cores 6a and 6b are adhered to the bottom edge portions of the core halves 1a and 1b, and 3a and 3b respectively. The magnetic circuit of the recording and/or reproducing core 1 is formed by the core halves 1a and 1b, and the back core 6a. The magnetic circuit of the erasing core 3 is formed by the core halves 3a and 3b and the back core 6b.
Reference numerals 11 and 12 in FIG. 1 denote sliders that support the recording and/or reproducing core 1 and the erasing core 3, respectively, to reinforce the cores 1 and 3 and at the same time to stabilize a facing relationship of the cores 1 and 3 with the magnetic disc. The sliders 11 and 12 have grooves 11b and 12b for accommodating the bobbins 7 and 9, respectively, so that their cross-sections are formed into a block with a substantially L-shaped profile. The upper surfaces of the sliders 11 and 12 are formed into facing surfaces 11a and 12a which face the magnetic disc. The sliders 11 and 12 are attached to the side surfaces of both the recording and/or reproducing core 1 and the erasing core 3, so that the overall arrangement of a magnetic head 15 is completed, as shown in FIG. 2.
As shown in FIG. 2, in the magnetic head 15, the portions of the sliders 11 and 12 are adhered and fixed to an elastic plate such as a gimbal spring 13 that functions as a supporting member. The magnetic head 15 is attached to a magnetic disc apparatus not shown through the elastic plate 13.
This elastic plate 13 has extended holes 13a formed substantially into an L-shape so as to surround a central portion of the plate 13. An opening 13b is formed into this central portion to engage the bottom portion of the magnetic head 15.
The terminals 8a and 8b, and 10a and 10b of the coils 8 and 10 of the magnetic head 15 are connected to a flexible printed circuit board 14 for connecting the magnetic head 15 to an external circuit.
FIG. 3 shows a magnetic head with a core arrangement known generally as a laminated type. The differences between this head and the head shown in FIGS. 1 and 2 are in the arrangement of the coil, the arrangement of the sliders and the position at which the coil is attached.
That is, a magnetic head 22 shown in FIG. 3 has two erasing cores denoted by reference numerals 3 and 3'. These erasing cores 3 and 3' are sandwiched and supported from both sides by sliders 20 and 21 interposing a spacer plate 17 having the same thickness as the recording and/or reproducing core 1. Furthermore, the recording and/or reproducing core 1 is sandwiched and supported by sliders 20 and 21 interposing spacer plates 16 and 16' having the same thickness as the erasing cores 3 and 3', respectively. Further, the recording and/or reproducing core 1 is adhered to the spacer plate 17, and the spacer plates 16 and 16' are adhered to the erasing cores 3 and 3', in such a way that seen from the direction of arrow A, the magnetic gaps 4 and 4' in the erasing cores 3 and 3' sandwich the magnetic gap 2 in the recording and/or reproducing core 1.
Moreover, the sliders 20 and 21 do not have grooves to accommodate the coils (bobbins) of both the cores as in the example described above, so that the sliders 20 and 21 are attached to the erasing cores 3 and 3' and the spacer plates 16 and 16' without gap. Accordingly, the coils not shown are engaged with portions of the cores protruding into the lower side of the elastic plate 13.
When reproducing is performed by the magnetic head having the arrangement described above, variations in environmental conditions may cause displacements in the relative positions between the magnetic head and the track on the magnetic disc, resulting in the following problems.
For example, when the recording and/or reproducing magnetic gap 2 is reproducing a track R1 on the magnetic disc on which data has already been recorded as shown in FIG. 4, this type of displacement in position may cause one or both of the erasing magnetic gaps 4 and 4' (in this example the gap 4) to be erroneously positioned on an adjacent track R2.
In such a situation, a reproducing magnetic flux from the track R2 will pass through the erasing core 3. The linkage of the magnetic flux to the coil 10 of the erasing core 3 will induce a voltage across the coil 10. That is, the erasing core 3 will erroneously cause reproduction of the signal on the track R2.
Furthermore, since the erasing core 3 and the recording and/or reproducing core 1 are extremely close to each other, the thus reproduced signal from the erasing core 3 will leak to the recording and/or reproducing core 1 as crosstalk and be picked up by that core. As a result, the signal from the track R1 and the signal from the adjacent track R2 will overlap in the recording and/or reproducing core 1 and be reproduced. This results in the problem of diminished reliability of the reproduced data.